One of the least intuitive features here on Steemit are the tags.
After putting hours of effort to writing a great post, agonising over the title and the first picture, that are going to catch peoples attention, tags are often an afterthought. But they are an essential element if you wish to get your post viewed and voted on.
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There is no strict rule but in general appropiate realted tags, you have a limit of 5 so use sparingly and the first one is what shows up in your feed as the main tag.
There are some tags which will get you included in competitions or initiatives from time to time.
Some examples
An initiative which I regularly tag is minnowsunite. The use of this tag will automatically result in upvotes according to a post by 
New comers should also be aware of the introduceyourself tag. Posting here gives new users the opportunity to introduce themselves to the community and begin to get a following. You might also get a boost from a whale or two if your lucky with a few big upvotes. Whales have been seen in these waters.
You can tag any post with any word, I have recently mistyped introduceyourelf as a tag. I hope I haven't disappointed people searching Steemit for elves. 😁 Using your own tags means you can sort your posts as you like at a later stage.
Sometimes you just want to get your post out there. A technique I use sometimes is to look at trending tags to see what is the top trending tags, what tags would get my post most viability?
Click on the top right of your blog home page (the three line button)
This gives a dropdown menu where you can select trending topics
Sort the trending topics by Payouts, Comments or Posts to find the top.
Here I have sorted by Payouts, It's now easy to choose relevant tags to add to my post that are related to the content in it.
For additional reading 
Please add comments to this post with any tags that your involved with and a link to the announcement post if possible. It might also be useful to point out here in the comments tags that are misused for the benefit of newer people to Steemit.
Thank you for reading this. I write on Steemit about Blockchain, Cryptocurrency, Travel and lots of random topics.
